The present invention relates to an apparatus for use in the deposition of a material, particularly a semiconductor material, from a liquid phase, e.g. liquid phase epitaxy. More particularly, the present invention relates to such an apparatus which includes temperature measuring means for achieving control of the saturation of the liquid with the material to be deposited.
One technique for depositing a single crystalline material on a substrate is liquid phase epitaxy. To carry out the deposition of a material by liquid phase epitaxy the material to be deposited is dissolved in a heated solvent, generally a molten metal, and the substrate is brought into contact with the solution. The solution is then cooled causing some of the material to be precipitated out of the solution and deposited on the surface of the substrate. To deposit a plurality of superimposed layers on a substrate, a type of apparatus has been developed which includes a furnace boat having a plurality of spaced wells therein, each of which is adapted to contain a deposition solution. A substrate carrying slide is movable through the furnace boat so as to bring the substrate into contact with the solution in each of the wells. U.S. Pat. No. 3,565,702 to H. Nelson, entitled "DEPOSITING SUCCESSIVE EPITAXIAL SEMICONDUCTIVE LAYERS FROM THE LIQUID PHASE", issued Feb. 23, 1971, shows one type of such a furnace boat in which the wells are arranged in a line and the slide moves longitudinally through the furnace boat and across the wells. There are other types of furnace boats in which the wells are arranged in a circle and the substrate carrying slide is rotated to carry the substrate into each of the wells.
For making various types of semiconductor devices by liquid phase epitaxy it is often desirable that the solution be exactly saturated with the semiconductor material at the time that the substrate is brought into contact with the solution. Another factor which must be controlled in the deposition of the layers of the material is the amount of the material in the solution in order to deposit a layer of a desired thickness. Thus, knowing the amount of material which must be dissolved in the solution to deposit a layer of a desired thickness, it is desirable to be able to determine when the solvent is at the temperature at which it will be exactly saturated with that amount of the material. This temperature is sufficiently critical that merely measuring the temperature of the furnace which contains the furnace boat is not adequate for determining the temperature of the solution.